The present disclosure relates to the field of pressure measurement, and relates more particularly to a pressure detection and measurement sensor including at least one resistive force-detector cell. The present disclosure further concerns, in particular, detecting and measuring pressures that are applied by the bodies of patients who are lying or sitting on healthcare support devices such as therapeutic mattresses, and in particular on support devices of the type comprising mattresses or cushions having inflatable cells, in order to regulate the inflation pressures of the cells of the support device so as to combat skin pathologies related to prolonged immobility on a bed or in a wheelchair, or in some other type of seat.
It is known, in medical practice, that interface pressures at the interfaces between patients' bodies and their support devices constitute the main factor in the development of skin complications, in particular, decubitus ulcers or “bedsores,” due to the patients being immobile for prolonged periods on their beds or in their wheelchairs or seats.
One of the tried and tested techniques for combating formation and development of bedsores in patients consists in supporting the patients on beds that include mattresses having inflatable cells, the inflation pressures of the cells being regulated as a function of the morphology and of the weight of the patient so as to minimize the interface pressures between the patient's body and the surface of the mattress.
The interface pressures are evaluated or measured, in particular, by means of sensors that can be of various technologies and that are generally placed under the inflatable cells of the mattresses on which the patients are recumbent.
Depending on the technology implemented for them, such sensors make it possible to determine either the “float line,” i.e. the distance to which the patient's body penetrates into the inflatable cells of the support device, or the pressures applied by the patient's body on the inflatable cells of the support device.
As a function of the response signal from the sensor, the penetration depth of or the pressure applied by the body on the support device is determined by an electronic control and regulation device and is compared with setpoint values that are predetermined as a function of the morphology of the patient. Whenever the depth or the pressure computed on the basis of the response signal from the sensor lies outside the range of setpoint values, the electronic control and regulation device actuates inflation means so as to adjust the inflation pressures of the inflatable cells of the support device so as to achieve support and comfort that are adapted to the morphology and to the position of the patient.
As indicated above, various sensors currently exist that have been specially developed to regulate inflation pressure of support devices having inflatable cells, such as therapeutic mattresses.
Mention can be made, in particular, of the Applicant's Documents FR-A-2 757 378 and WO-A-99 39 613 that describe respective sensors of distinct technologies.
Document FR-A-2 757 378 describes a support device having inflatable cells and provided with a control device including an inductive sensor placed under the inflatable cells of the mattress at the sacral zone of the patient. The inductive sensor makes it possible to measure a penetration distance of the body of a patient recumbent on the support device having the sensor, and to control means for inflating the cells so as to regulate the inflation pressures of the cells as a function of the penetration distance measured by the sensor.
A first drawback suffered by such an inductive sensor results from the high cost of manufacturing it, thereby having a considerable impact on the cost of the support device itself. Furthermore, such an inductive sensor has thickness of at least 5 centimeters (cm), which requires the support device incorporating it to have a large thickness, such a thickness making it more difficult to achieve safe coverage by the safety bars installed on the frame of the support device for the purpose of preventing falls.
Finally, it is necessary to ensure that such an inductive sensor satisfies the requirements of the standards relating to electromagnetic compatibility (EMC) because it is a sensor that generates an electromagnetic field.
Document WO-A-99 39 613 also presents a support device having inflatable cells for supporting the body of a patient. That support device is provided with a pressure sensor that itself includes an inflatable chamber inflated to a predetermined pressure. The sensor is received under the inflatable cells of the sacral zone for supporting the patient. Thus, the internal pressure of the inflatable chamber of the sensor varies with the pressure variations in the inflatable cells of the support device as a function of the morphology, of the weight, and of the movements of the patient on the support device. Electronic means then compare the respective pressures in the inflatable chamber of the sensor and in the inflatable cells of the support device and control the inflation means accordingly so as to regulate and adjust the inflation pressures inside the cells when the comparison of the pressures lies outside a predetermined range of setpoint values. In order to perform its sensing function, the sensor is filled with a fluid having low compressibility, e.g. silicone oil.
As with inductive sensors, a drawback with such a hydraulic (fluid-flow) sensor lies in the high cost of manufacturing it, thereby having a considerable impact on the cost of the support device itself. Furthermore, such a hydraulic sensor has thickness of at least 3 cm, which requires the support device incorporating it to have large thickness, such a thickness making it more difficult to achieve safe coverage by the safety bars installed on the frame of the support device for the purpose of preventing falls.
Finally, such a sensor having an inflatable chamber is heavy because it contains about 4 kilograms (kg) of silicone oil, which makes it difficult to handle.
The main problem with the various sensors and systems associated with regulating the inflation pressures of the cells of mattresses and of other support devices for therapeutic use is the cost of manufacturing them and of implementing them, that cost limiting use thereof to support devices that are used and operated in hospitals, in particular in departments specialized in care and treatment of patients having very reduced mobility and/or presenting high risks of developing bedsores.
In addition, sensors known from the prior art have their own structures that are generally complex, and they also require interfaces and electronic systems for making use of the measurements that are sophisticated, and that are not only expensive but also difficult to maintain, and difficult to alter or replace in the event of failure and/or of malfunction. It is then necessary to change the entire support device and not merely that element of the device that is defective, which is unpleasant for patients and particularly costly for hospitals.
Finally, the problem of the high cost of the sensors and systems for pressure regulation in existing support devices having inflatable cells currently rules out the use of such support devices for the vast majority of patients receiving healthcare treatment at home because public and private health insurance schemes generally refuse to pay or to reimburse the costs inherent to purchasing and using such support devices with inflatable cells.
There thus exists a major technical problem in designing and making a pressure sensor that is suitable for being used in support devices having inflatable cells, and in particular devices of the therapeutic mattress or therapeutic cushion type, in order to enable the pressures inside the cells to be regulated, and that has a cost very significantly lower than the costs of existing sensors and systems, while nevertheless procuring similar performance. Such a sensor is, in particular, desirable so as to reduce the costs of support devices and thus the costs of purchasing and of using them for home healthcare treatment.
A second technical problem also exists in making a sensor that is suitable for being used in support devices having inflatable cells in order to enable the pressures inside the cells to be regulated rapidly, and that is easy to replace in the event of failure or malfunctioning in systems for regulating existing support devices having inflatable cells.
Document U.S. Pat. No. 6,386,051 describes using a plurality of (in particular over 200) sensors having force sensitive resistors or FSR cells and organized into arrays over the entire top surface of a mattress, i.e. above the mattress, with a view to determining the posture of a patient on the mattress.
Document US-2006/0070456 also describes using a plurality of sensors (FSR sensors) applied to nearly the entire hard bed frame solely for the purpose of detecting the presence of a patient on the bed for alarm purposes.
It is also conventional to implement those types of FSR sensors in automobile seats. However, in that use too, the sole purpose is to detect whether or not the seat is occupied by a person, optionally while also determining the approximate weight of said person.
In the uses mentioned in those prior patents, the sensors are not required to deliver an analog signal with a sensitive and adapted response including a zone of signal linearity or proportionality as a function of the load exerted on the sensor. A logic (YES/NO) response is essentially all that is sought, i.e. contact or absence of contact on the sensor.
However, with the device disclosed herein, it is possible to enable the inflation of the cells of a mattress having inflatable cells and on which the patient is supported to be regulated as a function of the load detected by the sensor, and in particular by a single sensor located at a single zone of the mattress, in particular, in this example, the zone of the sacrum.
With the device disclosed herein, it should thus be possible, on the basis of the data relating to patient penetration into the mattress at that zone, as delivered by the sensor, in combination with the measurement of the internal pressure of the mattress, to deduce the penetration profile of the patient over the entire surface of the mattress.
In addition, with regard to the present disclosure, the sensor may be adapted to deliver responses that are usable, while also being placed under the mattress so as to avoid contact between the sensor and the patient, it being possible for such contact to cause bedsores, and, in particular, the sensor disclosed herein may be suitable for being placed between two mattress layers, under an upper layer made up of inflatable cells.
For this purpose, it is desired to provide a sensor that can give a response that is adapted in terms of sensitivity of an analog signal, having a zone of signal proportionality as a function of the load exerted on the sensor, for loads approximately in the range 40 kg to 210 kg (the weight of a person).
The impedance of an FSR varies as a function of the compression force per square centimeter (cm2) exerted on it, but its response curve as a function of the applied force is generally non-linear. There therefore exist very large variations in resistance for low stresses, and, conversely, at higher stresses, resistance variations that are smaller. This makes it difficult to obtain an analog signal, i.e. a signal that is proportional to the load exerted.